This invention relates to screwdrivers having a nosepiece to engage a work surface and through which nosepiece a guideway extends via which a screw is driven into the workpiece and, more particularly, to a nosepiece which is adapted for driving screws at an angle into the workpiece and, preferably, countersinking the screws.
Autofeed screwdrivers are known such as those taught in the present inventor""s U.S. Pat. No. 5,934,162 in which a nosepiece is adapted to engage a surface of a workpiece and a driver shaft is adapted to drive a screw past the nosepiece and into the workpiece. Many prior art autofeed screwdriving apparatus are particularly adapted to drive screws into a workpiece with the screw disposed normal to the surface of the workpiece. The present inventor has appreciated that disadvantages arise when many known screwdrivers and drivers of other fasteners such as nails and the like are utilized to drive screws at an angle into a workpiece other than normal. Disadvantages which arise include an inability to properly countersink a fastener driven at an angle into a workpiece, difficulties with the nosepiece slipping on the work surface when attempting to drive a fastener at an angle into the workpiece and difficulties with marking or marring the surfaces of finished workpieces by the engagement of the nosepieces. The present inventor has also appreciated that the nosepieces of many autofeed screwdriving mechanisms when used to drive screws at an angle to the normal to the surface of the workpiece have the disadvantage of significantly increasing the depth a screw must be driven to provide for proper countersinking.
The present inventor has also appreciated the disadvantage that the surface contacting portions of nosepieces of many autofeed fastener driving devices are of larger size and diameter than advantageous for driving of screws into the workpiece at an angle which varies from a normal to the surface of the workpiece.
To at least partially overcome these disadvantages of the previously known devices, the present invention provides a nosepiece for fastener driving tools with a contact surface for engagement with the workpiece with a rounded profile to facilitate driving fasteners at an angle into the workpiece. Preferably, the contact surface has a first radially innermost portion of the contact surface for engagement of the workpiece when a screw is being driven substantially normal to the surface of the workpiece and a second outer portion of the contact surface radially outwardly from the innermost portion which outer portion is adopted to engage the work surface when a screw is being driven at an angle other than substantially normal to the work surface, the characteristics of the innermost portion of the contact surface and outermost portion of the contact surface varying such that the outer portion provides resistance to slippage of the nosepiece on the work surface when a screw is being driven at an angle to the normal.
It is an object of the present invention to provide a nosepiece with a contact surface to contact a workpiece in normal operation sized so that on tilting of the nosepiece to drive a screw at an angle to the vertical into a workpiece, the distance a screw must be driven to be properly countersunk into a workpiece is minimized.
It is an object of the present invention to provide a nose for fastener driving devices which is adapted for driving fasteners into a workpiece at an angle to the normal.
It is an object to provide a nose for a screwdriver which facilitates driving screws into a workpiece at an angle between about 85xc2x0 and 70xc2x0 to a normal to the workpiece.
It is an object of the present invention to provide a nosepiece for fastener driving devices which reduces slippage of the nosepiece when used in driving screws at an angle to a normal to the work surface.
It is an object of the present invention to provide a fastener driving tool which minimizes the increased extent to which a fastener must be driven to properly countersink a fastener into a workpiece when the fastener is driven at an angle which is not normal to the surface of the workpiece.
Accordingly, in one of its aspects, the present invention provides a screwdriver comprising:
a nosepiece having a forward workpiece contact surface,
the nosepiece having a guideway extending forwardly therethrough opening forwardly through the contact surface as fastener exit opening,
an elongate driver shaft received in the guideway rotatable about an axis,
the driver shaft having a forward end to engage and drive a threaded fastener,
the driver shaft slidably received in the guideway for relative reciprocal sliding therein along the axis to drive a fastener out of the nosepiece via the fastener exit opening,
the contact surface extending from the fastener exit opening radially outwardly relative the axis and rearwardly,
the contact surface comprises a radially innermost zone adjacent the fastener exit opening, and an outer zone radially outward and rearward from the innermost zone, the outer zone includes friction enhancing protrusions,
each protrusion extending forwardly to a forward extent rearward of the forward extent of the inner zone wherein when the nosepiece is urged forwardly into a flat surface of a workpiece with the axis at an angle between normal to the flat surface of the workpiece and about five degrees to a normal to the flat surface of the workpiece,
the innermost zone alone engaging a flat surface of a workpiece and the outer zone and its protrusions not engaging the flat surface;
when the nosepiece is urged forwardly into a flat work surface of a workpiece with the axis at an angle of greater than five degrees to a normal to the flat surface the protrusions of the outer zone engaging the flat surface.
In another aspect, the present invention provides a screwdriver comprising:
a nosepiece having a forward workpiece contact surface,
the nosepiece having a guideway extending forwardly therethrough opening forwardly through the contact surface as fastener exit opening,
an elongate driver shaft received in the guideway rotatable about an axis,
the driver shaft having a forward end to engage and drive a threaded fastener,
the driver shaft slidably received in the guideway for relative reciprocal sliding therein along the axis to drive a fastener out of the nosepiece via the fastener exit opening,
the contact surface extending from the fastener exit opening radially outwardly relative the axis and rearwardly,
the guideway defining a generally cylindrical space coaxially about the axis having a diameter marginally greater than a head of a fastener to be driven and adapted to assist in locating a screw within the guideway coaxially aligned with the driver shaft,
wherein while maintaining the contact surface urged forwardly into constant engagement with a flat surface of a workpiece, on tilting the screwdriver from a position with the axis normal the flat surface to a position with the axis at an angle to the flat surface of not less than 70 degrees, the radially innermost points at which contact occurs between the contact surface and the flat surface are located on the contact surface a distance radially from the axis not greater than two times the diameter of the guideway.
Preferably, the contact surface is a segment of a spherical surface of a radius centered on the axis,
the radius of the spherical surface being not greater than about two times the diameter of the guideway.
More preferably, the exit opening lies in a plane normal the axis,
the contact surface lies rearward of the surface of a cone extending rearwardly at an angle of at most 45xc2x0 and centered on the axis at a point forward of a first point on the axis where the plane intersects the axis by at least one half a diameter of the guideway.